The zebrafish core will provide efficient and safe care for wild-type and mutant zebrafish that are studied by the investigators in this proposal. Initially, Core B will provide centralized reagents, methods and technology to the investigators for study of particular gene expression in wild-type embryos. As an epistasis analysis of blood forming mutants is undertaken, the core will provide a diverse set of mutant embyros for study. The core will be supervised by the PI (Dr. Leonard Zon), in collaboration with a technician after year one. Dr. Zon has experience in zebrafish biology. The zebrafish core may also be utilized to facilitate collaborations with other investigators in the Harvard Medical area.